1. Field of the Invention
The present invention relates to novel coated fertilizer granules which are coated with a carboxyl-carrying ethylene copolymer in which the carboxyl groups may also be in the form of their alkali metal, alkaline earth metal or ammonium salts, the carboxyl-carrying ethylene copolymer being composed of
a) from 75 to 90% by weight of ethylene and PA1 b) from 10 to 25% by weight of an .alpha.-olefinically unsaturated C.sub.3 -C.sub.8 -alkanecarboxylic acid, and those coated fertilizer granules which contain an active ingredient for crop protection being excepted. The present invention furthermore relates to a process for their preparation and to fertilizer application methods in which the novel coated fertilizer granules are used. PA1 a) from 70 to 90, preferably from 75 to 85, % by weight of ethylene and PA1 b) from 10 to 30, preferably from 15 to 25, % by weight of an .alpha.-olefinically unsaturated C.sub.3 -C.sub.8 -alkanecarboxylic acid.
2. Description of the Background
It is generally known that fertilizer granules which are coated with a water-impermeable layer of a polymer can be used as fertilizer. As a result of the coating, the efficiency of these fertilizers is increased because the coated fertilizer releases in a sustained manner the substances serving as plant nutrients and can thus display its action over a long period. Such slow-release fertilizers are described, for example, in Ullmann's Encyclopedia of Industrial Chemistry, 5th edition 1987, volume A 10, pages 363 to 369, and their advantages are summarized in Fert. Res. 35 (1993), 1-12.
U.S. Pat. No. 4,851,027 discloses the use of aqueous dispersions which contain a polymer having a glass transition temperature of 60.degree. C. or more for coating fertilizer granules. A large number of monomers, including ethylene and unsaturated carboxylic acids, such as acrylic acid and methacrylic acid, are specified as monomers which are suitable for the preparation of these polymers.
No specific information about the use of copolymers of ethylene and olefinically unsaturated carboxylic acids as coating polymers is given. EP-A-337 298 recommends the use of copolymers of ethylene, vinyl chloride and at least one monomer selected from the group consisting of acrylamide, methacrylamide, N-methylolacrylamide, N-butoxymethacrylamides, acrylic acid, glycidyl methacrylate and hydroxyethyl acrylate as coating polymers for coating fertilizer granules.
Japanese Preliminary Published Application 71 698/87 discloses coated fertilizer granules which are prepared by applying a solution or a dispersion of an ethylene/acrylic acid copolymer in which the solvent or the continuous phase is an organic solvent, for example a hydrocarbon.
The coated fertilizer granules have to meet a variety of requirements with regard to simple and economical preparation and their performance characteristics.
The polymers should be capable of being applied to the fertilizer granules without the use of organic solvents. Furthermore, the amount of polymer required for coating the granules should be very small in order to achieve an adequate slow-release effect.
In addition, the coated fertilizer granules should show no tendency to stick together, in particular at temperatures as usually occur during their storage or during transport, without special measures being necessary in this respect. On the other hand, the coating polymers must not be excessively hard and brittle, since the coats would otherwise be damaged or even flake off when the coated fertilizer granules are subjected to mechanical stress as occurs, for example, during transfer or broadcasting on the arable land.
Coated fertilizer granules which meet these complex requirements have not been disclosed to date. Only the non-prior-published German Patent Applications with the file reference P 43 43 176.2 describe coated fertilizer granules which contain a crop protection agent and whose coat consists of a polymer which is composed of from 75 to 90% by weight of ethylene and from 10 to 35 25% by weight of an .alpha.-olefinically unsaturated mono- or dicarboxylic acid.